Prevaporizing burner can



m 2 m O Y p m W7 E 0 H m mm a. .n A 7 7 3 M nu l u N m m m/w 5 3 J 2m 0nW? x Oct. 29, 1968 I in nu United States Patent 3,407,596 PREVAPORIZINGBURNER CAN Curt J. Dasbach, West Palm Beach, and Arno G. Kalb, LakePark, Fla., assignors, by mesne assignments, to the United States ofAmerica as represented by the Secretary of the Navy Filed Mar. 15, 1967,Ser. No. 624,121 4 Claims. (Cl. 60--39.71)

ABSTRACT OF THE DISCLOSURE A prevaporizing burner can apparatus havingan axially located annulus for distributing fuel in a vaporized state tothe flame Zone. For more efficient primary combustion, air from the mainair-stream flow is premixed with the fuel through apertures in a fuelnozzle guide and is admitted to the flame zone through radial passagesin the annulus. The passages also permit a further mixing of thefuel-air flow.

Background of the invention The present invention relates generally to acombustion apparatus in which combustion of liquid fuel is required tobe supported by a stream of air or other gas flowing through a duct witha flame-extinguishing velocity. More particularly, the instant inventionconcerns itself with a burner can or flame tube having means forprevaporizing the air-fuel mixture in order to adequately preheat andpremix the fuel in preparation for burning, as, for example, in gasturbine or other jet propulsion power units and in gas turbines forother purposes.

In order to achieve satisfactory operation of a combustion system over awide range of air mass flow and density requires that the flame shouldnot be extinguished under any conditions of operation. To obviate this,the range of air-fuel ratios over which burning will take place must beas wide as possible while maintaining combustion efficiency at areasonable level with weak mixture. It is also desirable for pressurelosses to be low and for an even temperature distribution over thecross-section of the flow to be achievable. Aside from preventing flameblow-out by the air flow, the attainment of a high standard of mixing asbetween the combustion air and the fuel to be burnt, and of atomizationand distribution in the case of a liquid fuel, is required. Atomizationmeans heretofore employed in gas turbine and similar combustion systemsincluded the injection of liquid fuel droplets into an almost stagnantregion protected by a baflle from the full blast effect of the air flow,with specially designed atomizing injection nozzles being provided toachieve a satisfactory spray of the fuel.

Recognizing the numerous drawbacks and inefiiciencies in such a fueldistribution technique, vaporization systerns came into being in anattempt to improve upon the standard of fuel-air mixing in preparationfor burning.

Summary of the invention The invention is directed to an improvementupon the existing apparatus employing a vaporizing means for mixing theair with fuel in preparation for burning. A nozzle guide acts to bothdirect fuel from the nozzle into a vaporizing annulus and through radialapertures therein, to initially admit air from the main airstream flowfor premixing it with the fuel. This premixed air-fuel flow is vaporizedfrom heat transfer through the outer wall of the annulus which is indirect exposure to and forms the inner wall of the burner can. Thedirection of the mixture in its fuel rich condition is reversed uponentering the annulus, led therethrough, and again reversed in directionand led to the primary combustion zone to form a flame around theprevaporizing passage. In order 3,407,596 Patented Oct. 29, 1968 tosupport primary combustion, penetration air from the main airstream flowis admitted into the burner can through passages provided in theannulus, which passages also serve to interrupt the fuel flow thereaboutfor further mixing. At the exit lip of the vaporizing annulus isprovided a double plate to obviate the problem of burning in this area.Also provided are clearances around the upstream passages, on theupstream side, to allow for differential thermal growth between theouter annulus wall which is in direct contact with'the flame in the canand the inner annulus wall.

It is therefore an object of the present invention to provide acombustion apparatus having a new and novel means for distributing fuelin .a vaporized state to the burner can or flame zone in a mannerwhereby a preheating and premixing of the fuel is effected inpreparation for burning 'both uncontaminated as well as c0ntami natedliquid fuel.

Another object of the present invention is to provide in a combustionapparatus a fuel distribution means employing larger internal flowpassages than heretofore used which are less sensitive to plugging dueto contaminants, less sensitive to variations in fuel flow and capableof more efficiently distributing the fuel without resulting in seriousprofileetfects such as streaks and hot spots.

Other objects, advantages and novel features of the present inventionwill become apparent from the following detailed description of theinvention when considered in conjunction with the accompanying drawings.

Brief description of the drawings FIG. 1 is a longitudinal section ofthe combustion apparatus according to the invention;

FIG. 2 is a sectional viewtaken at line 2-2 of FIG. 1; and

FIG. 3 is a view taken at line 3-3 of FIG. 1 showing an expansionclearance around one of the passages.

Description 0 the preferred embodiment Turning now to the drawingswherein like reference characters designate like or corresponding partsthroughout the several views, there is shown in FIG. 1 the combustionapparatus 10 according to the instant invention being axially supportedwithin an outer cylindrical duct or casing 11 carrying the mainairstream with the appparatus 10 so constructed so to interrupt the mainflow of air by reducing its velocity sufficiently to support combustionof injected fuel. The design of the combustion apparatus 10 includes aburner can 12 comprised of a plurality of conventional overlapped annuliwithin which is axially located a single spray nozzle 13 for sprayingfuel from a source, not shown, into a fuel guide 14 surrounding a partof nozzle 13 downstream thereof. Part of the air from the main airstreamflow is led into guide 14, as shown by arrows, through both the spacebetween nozzle 13 and guide 14 and through a plurality of radial holes15 provided in the guide for initially premixing the fuel with smallquantities of air. This fuel rich mixture is thrust into conical passage16 which reverses its direction and leads it radially outward to annulus17 which has an outer liner or wall 18 and an inner wall 19. Liner 18,as is evident from the drawings, also forms the inner wall of burner can12. The fuel vaporizes and is more intimately mixed with the air as itflows along conical passage 16 and upstream along the annulus orprevaporizing passage 17. This vaporization results from the heattransfer through liner 18 which is in direct contact with the flame inthe can. This heat transfer serves the dual purpose of preventing liner18 from becoming excessively hot while at the same time it provides theheat required to vaporize the fuel. As the fuel enters the dome section21 of the burner can, it is again reversed in direction by means ofcurved wall 20. The mixture, still in a fuelrich condition, at thispoint, is supplied with additional primary air just downstream of itsentry point to provide the proper mixture to begin burning. Thispenetration air for maintaining efficient combustion is supplied, asshown by arrows, through a series of primary combustion passages ortubes 22 located in liner 18 and extending through holes in wall 19. Arow of secondary combustion tubes or passages 23 are also providedacross annulus 17 in the same manner as tubes 22 in order to effectivelydilute the hot gases to obtain a more even burner temperature profileinto the turbine. Both passages 22 and 23 also act as baffles to aid inthe mixing of the prevaporized flow in annulus 17. The tubes were sized,figures omitted, by an iterative calculation in order to obtain apredetermined air flow at each respective axial combustion hole row byfirst assuming an overall combustion chamber pressure drop.

In FIG. 1, and more, plainly in FIG. 3, a radial and axial clearance 24is shown around the primary combustion tubes 22 to allow fordifferential thermal growth between inner wall 19 and outer liner 18 ofthe annulus. The outer liner 18, being directly exposed to thecombustion flame, will grow or expand more than wall 19. While noclearance is provided around the secondary combustion slot 23, agraduated clearance is provided about passages 22 on the upstream side.This graduated design will effectively compensate for any expansion ofliner 18 with respect to wall 19. Since the outer liner is fixedrelative to the inner liner at the secondary passage 23, it can onlygrow toward the front of the can relative to the inner liner, therebytaking up the clearance provided in the first three rows of holes. Anyleakage that occurs will be into the vaporizing annulus 17 since thepressure drop is in this direction. This leakage is not critical toburner can performance.

As shown in FIG. 1 of the drawings, a double plate 25 at the vaporizingannulus exit is provided to anticipate the problem of burning in thisarea. Since the fuel that exits the annulus 17 is all vaporized,combustion takes place close to this exit lip, Combustion experience hasshown that the thinner the material that is used to construct burner canliners the faster it will burn if it is exposed to the combustionflames.

In FIGS. 1 and 2, a plurality of apertures are radially located in eachof the overlapped burner can annuli in order to admit (as shown byarrows) an additional quantity of air from the main airstream flow forboth cooling burner can 12 and for supplying additional penetration airto the air-fuel mixture in the can. The flow of the remaining primaryair between duct 11 and burner can 12 is depicted by arrows. Also, forconvenience in initially starting the combustion, an ignition spark plughaving terminals 26 may be provided as shown.

The novel burner can according to the instant invention is useable for avariety of purposes. For example, it may be the essential part of theram-jet device or it may be connected between the compressor and theturbine of a gas-turbine plant. The burner can is also designed topermit the burning of uncontaminated fuel or of fuel contaminated withimpurities without serious profile effects such as streaks and hotspots. This may be attributed to a premixing and a more evendistribution of the fuel at the nozzle guide 14 and along the conicalpassage 16 before entering annulus 17 for vaporization. The normalcooling effect derived from the vaporization of the fuel is thereforeadequate in preventing hot spots and streaks in the vaporizing passage17 and in the conical passage 16 during combustion. Performance of theburner can has been herein rendered unimpaired since the fuel ispremixed and preheated before burning in a manner not heretoforedevised. In addition, the use of a single fuel supply nozzle versus amulti-nozzle supply simplifies the instant combustion apparatus andrenders it more eflicient in operation since larger internal fiowpassages are necessitated which are less sensitive to variations in fuelflow. The single fuel supply nozzle also simplifies the manifolddistribution system, thereby reducing blockage to air flow. This resultsin a more uniform air distribution to the critical downstream portion ofthe combustion apparatus in the vicinity of the conical passage and'theannulus or prevaporizing passage. The advantage of a more uniform exittemperature profile is herein accomplished because of a prevaporizationand premixing of the fuel with air before the introduction of thenecessary pentration air to adequately support combustion. Furthermore,since the heat of the burning gases serves to vaporize the fuel withmost of this vaporization taking place within the prevaporizing passage,a shorter axial burner can length and less weight in the burner can ismade possible.

Obviously many modifications and variations of the present invention arepossible in the light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims the inventionmay be practiced otherwise than as specifically described.

What is claimed is:

1. In a combustion apparatus comprising in combination an outer casinghaving an air inlet for receiving air from the main airstream flow, aburner can within said casing, a prevaporizing duct within and extendingalong said burner can and having an outlet into said burner can, apremixing passage within said prevaporizing duct having at one end aninlet to receive fuel and a predetermined amount of air from the mainairstreanr flow, and at the other end an outlet into said prevaporizingduct, said can, duct and passage together defining a flow path for thefuel which passes downstream along said passage to the outlet thereof,reverses direction to pass upstream along said prevaporizing duct to theoutlet thereof, and then reverses again to pass downstream into andalong said burner can, and ignition means in said burner can forinitiating combustion therein and accordingly, by heat transfer to thefuel flowing through said prevaporizing duct, vaporizing the fuelcarried therein after the fuel is premixed with air in said passage, theimprovement comprising rows of radially located hollow tubes disposedacross said prevaporizing duct and opening into the main airstream flowso as to both interrupt the fuel flow through said duct for furthermixing the fuel-air flow and to admit air from the main airstreamflowinto said burner can in order to permit efiicient primary combustion;and clearances provided around the upstream rows of said hollow tubes toallow for difierential thermal growth between said burner and saidprevaporizing duct. I

2. In the combustion apparatus of claim- 1 wherein said premixingpassage includes a nozzle guide having a plurality of apertures radiallylocated in its sidewall for allowing an initial premixing of fuel withsmall quantities of air, a

3. In the combustion apparatus of claim 2 further including a mainsingle fuel spray nozzle for injecting fuel into said premixing passage.I

4. In the combustion apparatus of claim 3 wherein a double plate isprovided at said duct outlet to prevent excessive burning thereof.

References Cited UNITED STATES PATENTS I 2,720,753 10/1955 Sharpe60.39.7l

JULIUS E. WEST, Primary Examiner.

